Protein kinases (PKs) are enzymes which catalyze the phosphorylation of specific serine, threonine or tyrosine residues in cellular proteins. These post-translational modifications of substrate proteins act as molecular switch regulating cell proliferation, activation and/or differentiation. Aberrant or excessive PK activity has been observed in many disease states including benign and malignant proliferative disorders. In many cases, it has been possible to treat diseases in vitro and in many cases in vivo, such as proliferative disorders, by making use of PK inhibitors.
The kinases fall largely into two groups, those specific for phosphorylating serine and threonine, and those specific for phosphorylating tyrosine. Some kinases, referred to as “dual specificity” kinases, are able to phosphorylate tyrosine as well as serine/threonine residues.
Protein kinases can also be characterized by their location within the cell. Some kinases are transmembrane receptor proteins capable of binding ligands external to the cell membrane. Binding the ligands alters the receptor protein kinase's catalytic activity. Others are non-receptor proteins lacking a transmembrane domain and yet others are ecto-kinases that have a catalytic domain on the extracellular (ecto) portion of a transmembrane protein or which are secreted as soluble extracellular proteins.
Many kinases are involved in regulatory cascades where their substrates may include other kinases whose activities are regulated by their phosphorylation state. Thus, activity of a downstream effector is modulated by phosphorylation resulting from activation of the pathway.
Receptor protein tyrosine kinases (RPTKs) are a sub-class of transmembrane-spanning receptors endowed with intrinsic, ligand-stimulatable tyrosine kinase activity. RPTK activity is tightly controlled. When mutated or altered structurally, RPTKs can become potent oncoproteins, causing cellular transformation. In principle, for all RPTKs involved in cancer, oncogenic deregulation results from relief or perturbation of one or several of the autocontrol mechanisms that ensure the normal repression of catalytic domains. More than half of the known RPTKs have been repeatedly found in either mutated or overexpressed forms associated with human malignancies (including sporadic cases; Blume-Jensen et al., Nature 411: 355-365 (2001)).
RPTK over expression leads to constitutive kinase activation by increasing the concentration of dimers. Examples are Neu/ErbB2 and epidermal growth factor receptor (EGFR), which are often amplified in breast and lung carcinomas and the fibroblast growth factors (FGFR) associated with skeletal and proliferative disorders (Blume-Jensen et al., 2001).
Angiogenesis is the mechanism by which new capillaries are formed from existing vessels. When required, the vascular system has the potential to generate new capillary networks in order to maintain the proper functioning of tissues and organs. In the adult, however, angiogenesis is fairly limited, occurring only in the process of wound healing and neovascularization of the endometrium during menstruation. See Merenmies et al., Cell Growth & Differentiation, 8, 3-10 (1997). On the other hand, unwanted angiogenesis is a hallmark of several diseases, such as retinopathies, psoriasis, rheumatoid arthritis, age-related macular degeneration (AMD), and cancer (solid tumors). Folkman, Nature Med., 1, 27-31 (1995). Protein kinases which have been shown to be involved in the angiogenic process include three members of the growth factor receptor tyrosine kinase family: VEGF-R2 (vascular endothelial growth factor receptor 2, also known as KDR (kinase insert domain receptor) and as FLK-1); FGF-R (fibroblast growth factor receptor); and TEK (also known as Tie-2).
TEK (also known as Tie-2) is a receptor tyrosine kinase expressed only on endothelial cells which has been shown to play a role in angiogenesis. The binding of the factor angiopoietin-1 results in autophosphorylation of the kinase domain of TEK and results in a signal transduction process which appears to mediate the interaction of endothelial cells with peri-endothelial support cells, thereby facilitating the maturation of newly formed blood vessels.
The factor angiopoietin-2, on the other hand, appears to antagonize the action of angiopoietin-1 on TEK and disrupts angiogenesis. Maisonpierre et al., Science, 277, 55-60 (1997).
Administration of Ad-ExTek, a soluble adenoviral expressed extracellular domain of Tie-2, inhibited tumour metastasis when delivered at the time of surgical excision of primary tumours in a clinically relevant mouse model of tumor metastasis (Lin et al., Proc Natl Acad Sci USA 95, 8829-8834 (1998)). The inhibition of Tie-2 function by ExTek may be a consequence of sequestration of the angiopoietin ligand and/or heterodimerisation with the native Tie-2 receptor. This study demonstrates that disruption of Tie-2 signalling pathways, first, may be well tolerated in healthy organisms and, second, may provide therapeutic benefit.
The Philadelphia Chromosome is a hallmark for chronic myelogenous leukaemia (CML) and carries a hybrid gene that contains N-terminal exons of the bcr gene and the major C-terminal part (exons 2-11) of the c-abl gene. The gene product is a 210 kD protein (p210 Bcr-Abl). The Abl-part of the Bcr-Abl protein contains the abl-tyrosine kinase which is tightly regulated in the wild type c-abl, but constitutively activated in the Bcr-Abl fusion protein. This deregulated tyrosine kinase interacts with multiple cellular signalling pathways leading to transformation and deregulated proliferation of the cells (Lugo et al., Science 247, 1079 [1990]).
Mutant forms of the Bcr-Abl protein have also been identified. A detailed review of Bcr-Abl mutant forms has been published (Cowan-Jones et al, Mini Reviews in Medicinal Chemistry, 2004, 4 285-299).
EphB4 (also named HTK) and its ligand, ephrinB2 (HTKL) have critical roles in establishing and determining vascular networks. On the venous epithelium, EphB4 is expressed specifically, while, during early stages of vascular development, ephrinB2 is specifically and reciprocally expressed on arterial endothelial cells. Dysfunctional genes lead to embryonic lethality in mice, and the embryos show identical defects in forming capillary connections in case of either defect ephrinB2 and EphB4. Both are expressed at the first site of hematopoiesis and vascular development during embryogenesis. An essential role for proper hematopoietic, endothelial, hemangioblast and primitive mesoderm development was established. EphB4 deficiency results in an alteration in the mesodermal differentiation outcome of embryonic stem cells. Ectopic expression of EphB4 in mammary tissue results in disordered architecture, abnormal tissue function and a predisposition to malignancy (see e.g. N. Munarini et al., J. Cell. Sci. 115, 25-37 (2002)). From these and other data, it has been concluded that inadequate EphB4 expression may be involved in the formation of malignancies and thus that inhibition of EphB4 can be expected to be a tool to combat malignancies, e.g. cancer and the like.
c-Src (also known as p60 c-Src) is cytosolic, non-receptor tyrosine kinase. c-Src is involved in the transduction of mitogenic signals from a number of polypeptide growth factors such as epidermal growth factor (EGF) and platelet-derived growth factor (PDGF). c-Src is over expressed in mammary cancers, pancreatic cancers, neuroblastomas, and others. Mutant c-Src has been identified in human colon cancer. c-Src phosphorylates a number of proteins that are involved in regulating cross-talk between the extracellular matrix and the cytoplasmic actin cytoskeleton. Modulation cSrc activity could have implications in diseases relating to cell proliferation, differentiation and death. See Bjorge, J. D., et. al. (2000) Oncogene 19(49):5620-5635; Halpern, M. S., et. al. (1996) Proc. Natl. Acad. Sci. U.S.A. 93(2), 824-7; Belsches, A. P., et. al. (1997) Frontiers in Bioscience [Electronic Publication] 2:D501-D518; Zhan, X., et. al (2001) Chemical Reviews 101:2477-2496; Haskell, M. D., et. al. (2001) Chemical Reviews 101:2425-2440.
The fms-like tyrosine kinase 3 (FLT3) receptor tyrosine kinase is now recognized to be a critical mediator in the pathogenesis of myeloid and some lymphoid leukemias. Activation of FLT3 on leukemic cells by FLT3 ligand leads to receptor dimerization and signal transduction in pathways that promote cell growth and inhibit apoptosis (Blood, Vol. 98, No. 3, pp. 885-887 (2001)).
Use of tyrosine kinase inhibitors for AML therapy is hindered by the acquisition of mutations in the kinase catalytic domain, and in the case of BCR-ABL, these mutations confer resistance to imatinib.
FLT3 is widely expressed in AML and some cases of acute lymphocytic leukemia. Activating mutations in FLT3 confer a poor risk in patients with AML. Thus, FLT3 is a promising target for therapeutic intervention.
Platelet-derived growth factor receptor (PDGFR) tyrosine kinase is expressed in a number of tumours such as small-cell lung cancer, prostate cancer, and glioblastoma as well as in the stromal and vascular compartments of many tumors. Expression of both PDGF and PDGF receptors (PDGFRs) has been observed in pancreatic cancer (Ebert M et al., Int J Cancer, 62:529-535 (1995).
Fibroblast Growth Factors
Normal growth, as well as tissue repair and remodeling, require specific and delicate control of activating growth factors and their receptors. Fibroblast Growth Factors (FGFs) constitute a family of over twenty structurally related polypeptides that are developmentally regulated and expressed in a wide variety of tissues. FGFs stimulate proliferation, cell migration and differentiation and play a major role in skeletal and limb development, wound healing, tissue repair, hematopoiesis, angiogenesis, and tumorigenesis (reviewed in Ornitz, Novartis Found Svmp 232: 63-76; discussion 76-80, 272-82 (2001)).
The biological action of FGFs is mediated by specific cell surface receptors belonging to the RPTK family of protein kinases. These proteins consist of an extracellular ligand binding domain, a single transmembrane domain and an intracellular tyrosine kinase domain which undergoes phosphorylation upon binding of FGF. Four FGFRs have been identified to date: FGFR1 (also called Flg, fms-like gene, fit-2, bFGFR, N-bFGFR or Cek1), FGFR2 (also called Bek-Bacterial Expressed Kinase-, KGFR, Ksam, Ksaml and Cek3), FGFR3 (also called Cek2) and FGFR4. All mature FGFRs share a common structure consisting of an amino terminal signal peptide, three extracellular immunoglobulin-like domains (Ig domain I, Ig domain II, Ig domain III), with an acidic region between Ig domains (the “acidic box” domain), a transmembrane domain, and intracellular kinase domains (Ullrich and Schlessinger, Cell 61: 203, 1990; Johnson and Williams (1992) Adv. Cancer Res. 60: 1-41). The distinct FGFR isoforms have different binding affinities for the different FGF ligands, thus FGF8 (androgen-induced growth factor) and FGF9 (glial activating factor) appear to have increased selectivity for FGFR3 (Chellaiah et al. J Biol. Chem 1994; 269: 11620).
Another major class of cell surface binding sites includes binding sites for heparan sulfateproteoglycans (HSPG) that are required for high affinity interaction and activation of all members of the FGF family. Tissue-specific expression of heparan sulfate structural variants confer ligand-receptor specificity and activity of FGFs
FGFR-Related Diseases
Recent discoveries show that a growing number of skeletal abnormalities, including achondroplasia, the most common form of human dwarfism, result from mutations in FGFRs.
Specific point mutations in different domains of FGFR3 are associated with autosomal dominant human skeletal disorders including hypochondroplasia, severe achondroplasia with developmental delay and acanthosis nigricans (SADDAN) and thanatophoric dysplasia (TD) (Cappellen et al., Nature Genetics, 23: 18-20 (1999); Webster et al., Trends Genetics 13 (5): 178-182 (1997); Tavormina et al., Am. J. Hum. Genet., 64: 722-731 (1999)). FGFR3 mutations have also been described in two craniosynostosis phenotypes: Muenke coronal craniosynostosis (Bellus et al., Nature Genetics, 14: 174-176 (1996); Muenke et al., Am. J. Hum. Genet., 60:555-564 (1997)) and Crouzon syndrome with acanthosis nigricans (Meyers et al., Nature Genetics, 11: 462-464 (1995)). Crouzon syndrome is associated with specific point mutations in FGFR2 and both familial and sporadic forms of Pfeiffer syndrome are associated with mutations in FGFR1 and FGFR2 (Galvin et al., PNAS USA, 93: 7894-7899 (1996); Schell et al., Hum Mol Gen, 4: 323-328 (1995)). Mutations in FGFRs result in constitutive activation of the mutated receptors and increased receptor protein tyrosine kinase activity, rendering cells and tissue unable to differentiate.
Specifically, the achondroplasia mutation results in enhanced stability of the mutated receptor, dissociating receptor activation from down-regulation, leading to restrained chondrocyte maturation and bone growth inhibition (reviewed in Vajo et al., Endocrine Reviews, 21(1): 23-39 (2000)).
There is accumulating evidence for mutations activating FGFR3 in various types of cancer.
Constitutively activated FGFR3 in two common epithelial cancers, bladder and cervix, as well as in multiple myeloma, is the first evidence of an oncogenic role for FGFR3 in carcinomas. In addition, a very recent study reports the presence of FGFR3 activating mutations in a large proportion of benign skin tumors (Logie et al., Hum Mol Genet 2005). FGFR3 currently appears to be the most frequently mutated oncogene in bladder cancer where it is mutated in almost 50% of the total bladder cancer cases and in about 70% of cases having superficial bladder tumors (Cappellen, et al., Nature Genetics 1999, 23; 19-20; van Rhijn, et al., Cancer Research 2001, 61: 1265-1268; Billerey, et al, Am. J. Pathol. 2001, 158:1955-1959, WO 2004/085676). FGFR3 aberrant overexpression as a consequence of the chromosomal translocation t(4, 14) is reported in 10-25% of multiple myeloma cases (Chesi et al., Nature Genetics 1997, 16: 260-264; Richelda et al., Blood 1997, 90:4061-4070; Sibley et al., BJH 2002, 118: 514-520; Santra et al., Blood 2003, 101: 2374-2476). FGFR3 activating mutations are seen in 5-10% of multiple myelomas with t(4, 14) and are associated with tumor progression (Chesi et al., Nature Genetics 1997, 16: 260-264; Chesi et al., Blood, 97 (3): 729-736 (2001); Intini, et al, BJH 2001, 114: 362-364).
In this context, the consequences of FGFR3 signaling appear to be cell type-specific. In chondrocytes, FGFR3 hyperactivation results in growth inhibition (reviewed in Omitz, 2001), whereas in the myeloma cell it contributes to tumor progression (Chesi et al., 2001).
The inhibition of FGFR3 activity has been found to represent a means for treating T cell mediated inflammatory or autoimmune diseases, as for example in treatment of T-cell mediated inflammatory or autoimmune diseases including but not limited to rheumatoid arthritis (RA), collagen II arthritis, multiple sclerosis (MS), systemic lupus erythematosus (SLE), psoriasis, juvenile onset diabetes, Sjogren's disease, thyroid disease, sarcoidosis, autoimmune uveitis, inflammatory bowel disease (Crohn's and ulcerative colitis), celiac disease and myasthenia gravis. See WO 2004/110487.
Disorders resulting from FGFR3 mutations are described also in WO 03/023004 and WO 02/102972.
Gene amplification and/or overexpression of FGFR1, FGFR2 and FGFR4 has been implicated in breast cancer (Penault-Llorca et al., Int J Cancer 1995; Theillet et al., Genes Chrom. Cancer 1993; Adnane et al., Oncogene 1991; Jaakola et al., Int J Cancer 1993; Yamada et al., Neuro Res 2002). Overexpression of FGFR1 and FGFR4 is also associated with pancreatic adenocarcinomas and astrocytomas (Kobrin et al., Cancer Research 1993; Yamanaka et al., Cancer Research 1993; Shah et al., Oncogene 2002; Yamaguchi et al., PNAS 1994; Yamada et al., Neuro Res 2002). Prostate cancer has also been related to FGFR1 overexpression (Giri et al., Clin Cancer Res 1999).
There is an unmet need for highly selective molecules capable of blocking aberrant constitutive receptor protein tyrosine kinase activity, in particular FGFR activity, thereby addressing the clinical manifestations associated with the above-mentioned mutations, and modulating various biological functions.
In view of the large number of protein kinase inhibitors and the multitude of proliferative and other PK-related diseases, there is an ever-existing need to provide novel classes of compounds that are useful as PK inhibitors and thus in the treatment of these Protein Tyrosine Kinase (PTK) related diseases. What is required are new classes of pharmaceutically advantageous PK inhibiting compounds.
Epidermal Growth Factor Family and Related Diseases
The epidermal growth factor receptor (EGF-R) and ErbB-2 kinase are protein tyrosine kinase receptors which, together with their family members ErbB-3 and ErbB-4, play a key role in signal transmission in a large number of mammalian cells, including human cells, especially epithelial cells, cells of the immune system and cells of the central and peripheral nervous system. For example, in various cell types, EGF-induced activation of receptor-associated protein tyrosine kinase is a prerequisite for cell division and hence for the proliferation of the cell population. Most importantly, overexpression of the EGF-R (HER-1) and/or ErbB-2 (HER-2) has been observed in substantial fractions of many human tumours. EGF-R, e.g., was found to be overexpressed in non small-cell lung cancers, squameous carcinoma (head and neck), breast, gastric, ovarian, colon and prostate cancers as well as in gliomas. ErbB-2 was found to be overexpressed in squameous carcinoma (head and neck), breast, gastric, and ovarian cancers as well as in gliomas.
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